Most traditional key-depression digital locks are of the electronic/mechanical type with complicated structure. Wiring is usually necessary upon installation and the costs of both manufacturing and installation are comparatively high. The lock will be dead during a circuit trouble or power failure, this being the main drawback. Some sorts of key-depression digital locks have been disclosed recently, however, their constructions are rather complicated with unusually high cost and comparatively low reliability. The change of digital combination can only be effected by a skilled worker with special tools. Besides, only four digits are usually adopted hence their number of combinations is quite limited.